Conventional approaches used in RAID (redundant array of inexpensive drives) storage systems are primarily based on either an XOR function (parity calculations) or a mirror function to obtain redundancy and provide fault-tolerance. In RAID 1 and RAID 10 technologies, the drives are mirrored to obtain redundancy. Every time a new write occurs on the media, the entire data needs to be replicated and written onto both a data drive and a corresponding mirrored drive.
Referring to FIG. 1, a RAID 10 approach is shown. The drive DISK0 is shown mirrored to the drive DISK1. The drive DISK2 is shown mirrored to the drive DISK3. RAID 1 and RAID 10 approaches involve mirroring the complete contents of one drive to another drive. If there are two drives configured as RAID 1, where each drive has a capacity C GB, then the total capacity of the RAID group would be C GB (i.e., not the total capacity of both drives of 2 C GB). Hence, the overall storage capacity of a RAID 1 or RAID 10 is 50% of the total capacity of all of the drives in the RAID 1 or RAID 10 configuration.
Referring to FIG. 2, a RAID 4 and a RAID 5 approach are shown. A number of drives DISK0, DISK1, DISK2 and DISK3 are shown. In RAID 4 and RAID 5, the data blocks are striped across a number of the drives DISK0-DISK3 of the RAID group. In the RAID 4 configuration shown, the drives DISK0, DISK1 and DISK2 store data. The parity block is stored in a dedicated drive (i.e., shown as the drive DISK3). In a RAID 5, the parity is distributed across all the drives DISK0-DISK4 in the RAID group. In the RAID 5 configuration shown, the drive DISK3 is shown holding data (compared with a RAID 4 where the drive DISK3 only holds parity).
A D parity (i.e., a parity of the data block D) is stored in the disk DISK0. A C parity is stored on the DISK2. A B parity is shown stored on the disk DISK2. An A parity is shown stored on the disk DISK3.
RAID 4 and RAID 5 approaches use parity generation based on an XOR function. With RAID 4 and RAID 5, every stripe of data is used to generate parity. The parity generated is then stored in another dedicated drive or distributed across all the drives of the RAID group. RAID 4 and RAID 5 can tolerate only one drive failure at a time without losing data.
Referring to FIG. 3, a RAID 6 approach is shown. In a RAID 6 approach, the data blocks A-D are striped across a number of drives (i.e., shown as the drives DISK0-DISK4) of the RAID group. Two parities are calculated. The two parities are then distributed across all the drives in the RAID group. A first of the D parities (i.e., a parity of the data block D) is shown stored on the drive DISK0. A second of the D parities is shown stored on the drive DISK1. The A-C parities are shown similarly distributed on the drives DISK1-DISK4.
The performance of a RAID 6 configuration is less than the performance of a RAID 0, RAID 4 or RAID 5 configuration due to the dual parity generation. The complexity involved during data modification and data writes of a RAID 6 configuration also slows performance. A RAID 6 configuration can only provide a fault-tolerance of up to 2 drive failures without losing data.
It would be desirable to implement a method to establish a higher level of redundancy and fault tolerance than RAID level 6 without increasing the processing overhead of implementing parity.